It is known to control the position of a leading floor cutter of a plough in order to define the cutting level of the plough. Unless the floor cutter is set correctly the plough tends to climb or dip relative to the floor level. From DE No. 3508058 it is known to control the floor cutters of a plough by a radio telegraphic link between the plough and a control station. In this known arrangement, the plough has hydraulic actuators for adjusting the carriers of the floor cutters. Sensors on these displaceable carriers of the floor cutters detect the positions of the carriers and provide measurement signals which are relayed back to the control station. Any necessary correction of the leading floor cutter is then carried out. Although this known control method allows adjustment and re-adjustment of the floor cutters when the plough is running along the face, i.e. without halting the plough, the cutters are only controlled by sight or on an empirical basis.
To measure the plough cutting horizon with accuracy it is known in general to use probes or sensors which determine the position of the junction or interface between the mineral face or seam and the floor. DE No. 3509868 describes the use of such sensors. In such a control method, the height of the leading floor cutter is adjusted as a function of the seam and floor interface relative to the plough body during each run of the plough and over the entire run producing a relatively rigid and energy-consuming mode of operation. The reliability of operation of this known system can cause problems. To supply the actuators with pressure fluid, a hydropneumatic accumulator is built onto the plough. This accumulator needs to be relatively large in order to provide adequate hydraulic energy. To charge the accumulator a reciprocating pump is included in the drive chain for the plough. Since there is limited space for such a pump its size must be modest and the energy provided is then not sufficient to supply the accumulator without halting the plough and recharging the accumulator from an external source. An electrical power source for energizing the necessary control valves is also provided on the plough but again since the valves switch frequently the power source sometimes requires recharging or replacement involving further halting of the plough.